This invention relates to powder spray systems, and, more particularly, to an apparatus which, in the presently preferred embodiment, is operable to apply a solid particulate powder coating to the interior surface of a target object.
Powder coating materials are commonly used to coat or paint objects in industrial finishing applications. In such applications, a powder material, such as epoxy, polyester or porcelain frit, is conveyed to an applicator gun by air under pressure, and is ejected from the nozzle of the gun while entrained in an air stream. Quite commonly, an electrical charge is imparted to the powder as the air entrained powder is dispensed from the gun. This charge causes the powder to be electrostatically attracted toward the object to be coated which is generally at electrically ground potential. After coating, the object is usually moved into an oven where the powder coating material is melted and baked onto the coated surface.
In addition to providing a surface finish to objects, powder coatings have also been applied for other purposes, as for example, as lubricants in particulate powder form upon the surfaces of mold cavities to obtain a smooth, continuous surface on the molded part.
Powder spray guns used for spraying solid particulate powder materials generally include a handle connected to a barrel having a nozzle assembly at one end. The barrel is formed with a powder delivery passageway for transporting solid particulate powder to the nozzle assembly, and a passageway in which a high voltage cable is disposed which terminates with a charging electrode at the nozzle assembly. The solid particulate powder entrained in a stream of air flows through the powder passageway in the barrel along a path substantially parallel to its longitudinal axis, and then exits the barrel through the nozzle assembly where an electrostatic charge is imparted to the particulate powder by the charging electrode. One example of powder spray guns of this type is disclosed in the assignee's U.S. Pat. No. 4,380,320.
Standard powder spray guns such as described above, generally release the particulate powder from the nozzle assembly along an axis generally parallel to the direction of flow of the powder through the powder delivery passageway in the gun barrel. In some cases, a deflector is mounted in the nozzle assembly of the gun which contacts the stream of powder and deflects it at an angle to form a conical shaped spray pattern directed toward the surface of the object to be coated. Even with the spray pattern altered in this manner, the general direction of the powder spray is parallel to the longitudinal axis of the gun barrel. It has been found that in some applications, space limitations make it difficult to effectively coat the entire surface area of a target object with conventional powder spray guns. For example, the interior corners of closed rectangular or square boxes can be difficult to completely coat with known powder spray guns. If space limitations do not permit the barrel of the gun to be tilted so that the nozzle can be movably directed at different areas of a box interior, the interior corners of a box cannot be completely coated. This is because the spray pattern of conventional powder spray guns is directed parallel to the longitudinal axis of the gun barrel and not at varying angles relative to its longitudinal axis.
Modifications of known powder spray guns have been made to obtain complete coating of the interior surfaces of containers and other applications where space limitations restrict movement of the spray gun. In one design, the end of the gun barrel is turned upwardly at a sharp 90.degree. angle so that the nozzle discharges the particulate powder material perpendicularly relative to the longitudinal axis of the powder delivery passageway in the gun barrel. The problem with this design is that powder becomes entrapped and collects in the sharply angled bend of the gun barrel which causes clogging of the powder flow and results in the discharge of an uneven spray pattern of powder from the nozzle.
In an attempt to solve this problem, powder spray guns have been provided with a tubular extension having an inlet end adapted to fit onto the nozzle end of the gun barrel and an outlet end adapted to spray the powder material onto a target object. These extensions are gradually bent or curved between their inlet and outlet ends so that the outlet end is disposed approximately perpendicularly relative to the inlet end and the longitudinal axis of the powder delivery passageway in the gun barrel. Curved powder spray gun extensions reduce the powder clogging problems encountered with sharp 90.degree. bends in the powder flow path, but the extensions are incapable of permitting adjustment of the angle or direction in which the particulate powder material is released from their discharge end. While discharge of the powder material from the extension at an angle of 90.degree. relative to the longitudinal axis of the barrel permits coating of a portion of the interior surfaces of a target object which cannot be reached with conventional spray guns, other angular positions of the barrel extension may be necessary to completely coat other portions of the interior of the same object or a different target object. Several extensions could be formed at angles other than 90.degree., but this would require a manufacturer to stock a number of individual extensions having different angles to completely coat the interior surfaces of one or more target objects.
It has therefore been an objective of this invention to provide a powder spray gun capable of spraying solid particulate powder material entrained in a stream of air over the entire interior surface of containers or over the surface of target objects in a confined area.